An electro-photographic image forming apparatus such as a laser printer includes a scanner unit which performs an exposure process by irradiating beams to a photosensitive member (image carrier) (for example, see JP-A-8-191546). The image forming apparatus includes a body frame having a pair of lateral sidewalls. The scanner unit is disposed on a scanner supporting plate which is horizontally supported above between the pair of sidewalls. A top surface of the scanner unit is covered with a resin outer cover.